Denim fabric has been decolorized to produce an aesthetically pleasing decolorized look or fashionably faded look. Two major means used for such decolorization are stones and bleaches. Stones such as pumice stones are used to create a used and abused appearance in denim fabric through a physical washing of the denim fabric with stones or rocks having an abrasive surface. Alternatively, bleaches such as potassium permanganate, peroxide, or hypochlorite are used with or without stones to decolorize or discolorize the surface of denim fabric.
FIG. 1 shows a conventional fabric decolorization method which comprises a dry process S110, a desize process S120, an optional resin process S130, an abrasion process S140, a decolorization process S150, a local decolorization process S160 and a finish process S170.
Dry process S110 is first performed on garments to achieve used or worn out look, and the dry process includes hand sand, whisker, grinding and laser operation. After the dry process S110, the desize process S120 is conducted to remove starch from the raw fabric. In this process S120, enzymes such as amylase enzyme, lubricant and/or wetting may be applied to the fabric and then, the fabric is rinsed. After the desize process S120, the resin process S130 may or may not be performed. The resin process S130 is to achieve three dimensional rigid look in the fabric and can be done by the processes of resin dip or spray, dry and resin cure.
Then, the abrasion process S140 is conducted on the fabric using stone, superstone (like sand), and/or neutral enzyme. Then, the fabric is rinsed and dried. After the abrasion process S140, the decolorization process S150 and the local decolorization process S160 are conducted on the fabric. The decolorization process S150 is performed on the overall areas of the garments whereas the local decolorization process S160 is conducted on desired areas of the garments. Bleach or potassium permanganate is applied and then, the garments are neutralized using chemicals such as sodium meta bisulfate.
Pumice stones are widely used for the abrasion process and adding pumice stones gives the additional effect of a faded or worn look, especially at the seam allowance or on stitches. The pumice abrades the surface of the garments like sandpaper, removing some dye particles from the surfaces of the yarn.
Bleaching gives garments a more used look and brighter complexion and is usually carried out by strong oxidizing agents such as potassium permanganate, hypochlorite, or peroxide. Bleaching may be performed on the garments in overall or selectively using a spray. Oxidation has to be followed by neutralization because the remaining bleach will keep on damaging the fabric.
Lastly, the finish process S170 is performed. Pocket white, softener and/or tint may be applied to the garments. Laccase enzyme may be used for a special effect and rewashing with bleach or potassium permanganate followed by neutralization may be optionally conducted.
While the denim garments are decolorized, high quantities of indigo dye are separated and they soil weft threads, inside pockets as well as labels. To prevent this backstaining, pocket white is used to separate indigo. Pocket white may be applied in every treatment phase on the denim fabric. The application of pocket white during stone washing or separate after-washing leads to a reduction of the backstaining.
A number of problems have been presented by the use of stones and/or bleaches. First, the use of stones creates a considerable amount of damage to the denim products and the machine used for the stone washing process and a lot of time and labor have to be spent to remove stones and rocks in pockets, creases, and interior folds of the garment and in the machine. All the suspended solid of stone debris goes down to the wastewater and this makes it more costly to dump the wastewater to the sanitation system. Furthermore, the stone abrasion process is not selective and everything in the machines gets abraded whether it's a garment, a metal button or a rivet on the garments. This significantly reduces the quality of the garments.
Besides, use of bleach or potassium permanganate requires the neutralization process because the remaining bleach or oxidative will continue to damage the garments and affect the shade and color of the garments. Additionally, the use of bleach or potassium permanganate may cause environmental problems by increasing suspended solids and chemical oxygen demand in wastewater as well as the volume of wastewater itself. These increases will lead to increased time and cost to treat wastewater because suspended solids in wastewater always have to be treated and environmental regulations have put severe stress on the textile industry to control pollution by wastewater treatment and disposing of the used pumice stones.
For the case of decolorizing t-shirts, there are several ways to dye t-shirts: direct dyeing, pigment dyeing, sulfur dyeing and reactive dyeing. Reactive dyeing uses a chemical reaction to dye a t-shirt. Stones or bleaches may be used to decolorize t-shirts if they are dyed by direct dyeing or pigment dyeing. Even if reactive dyeing produces vibrant colors of a t-shirt, there is no conventional way to decolorize t-shirts with reactive dyeing.
Accordingly, to solve the above problems, a need for a method for decolorizing a dyed denim fabric through a dry ozone process to obtain an aesthetically pleasing decolorized look or fashionably faded look in the denim fabric has been present for a long time considering the expansive demands in the everyday life. This invention is directed to solve these problems and satisfy the long-felt need.